I like swimming as a "move slowly" because I simply enjoy being in the water, but definitely, for someone recovering from that sort of injury, it would be a good option to either swim or do water walking. I know after my knee injury that I could easily aggravate it until it was properly rehabbed, and being in water felt good because it took some of the strain off.
That said, keep working at building up walking and biking. My physio had me do the stationary bike for a while because it did help improve strength and mobility along with my other exercises, even if it was only for a few minutes a day. You'll gradually be able to do more if you work it over time. Ideally, you want to work until it is tired (maybe slightly achy) but not seriously painful.